Personal computers have become commonplace and many personal computers contain a rigid memory disk or hard drive. A very popular type of hard drive contains a thin- film metal coated rigid disk as the substrate of the magnetic media. The thin film rigid disks are typically manufactured by electroless nickel plating an aluminum substrate with a metal or metal alloy coating such as nickel/phosphorus. The nickel/phosphorus coating is then polished to a very fine, mirror-like finish. After polishing, the nickel/phosphorus coating is textured, followed by the application of a magnetic coating.
The texturing portion of this process is critical to the performance of the rigid disks. The texturing process preferably results in a random pattern of scratches with sharply defined edges in a substantially circumferential direction relative to the center of the rigid disk.
Texturing accomplishes a number of purposes It improves the aerodynamics between the computer head (which reads and writes data on the disk) and the thin film rigid disk as the disk spins beneath the head. It also improves the magnetic properties of the coated disks. The scratches formed during texturing make it easier for the head to distinguish bytes of information between tracks on the disk. If the scratches are too wide or too deep, however, there may be a potential loss of data off of the rigid disk. The texturing also eases the separation between the computer head and the rigid disk when the computer is first turned on. When the computer is turned off, the rigid disk and computer head are in contact with each other. When the computer is turned on, the rigid disk will begin to spin. If the disk is smooth and not textured, this head/disk contact makes it difficult for the disk to start spinning. This is known in the computer industry as stiction/friction.
The texturing process is traditionally accomplished by using a loose abrasive slurry. The loose abrasive slurries do provide substantially circumferential scratches that have sharply defined edges and are of the required depth. Loose abrasive slurries are, however, accompanied by a number of disadvantages. First, the loose abrasive slurries create a large amount of debris and waste. As a result, the thin film rigid disks must be thoroughly cleaned to remove any residue left on their surface from the abrasive slurry The loose abrasive slurry also results in a relatively high amount of wear on the equipment used for texturing.
To overcome the disadvantages associated with loose abrasive slurries, coated abrasive lapping films have been used to texture the thin film rigid disks. An example of such a product is IMPERIAL.TM. Lapping Film (Type R3) commercially available from 3M Company, St. Paul, Minn. This lapping film comprises a polymeric film backing having an abrasive coating bonded thereto. The abrasive coating consists of very fine abrasive particles (average particle size is less than 10 .mu.m) dispersed through a binder on the polymeric film. During use, the lapping film abrades a portion of the metal coating, thereby texturing the coating.
This process may also include disadvantages. The portion of the metal or metal alloy coating abraded away during texturing is known in the industry as swarf. The swarf generated during the use of lapping films and other abrasive articles with sealed backings can become attached to the high spots on the textured metal or metal alloy coating. That particular phenomenon is known in the industry as reweld. Those high spots can be hit by the computer head during use, which can cause a loss of data and/or head damage.
In addition to the problems with reweld, the lapping film may not provide scratches having edges as sharp and/or clean as those produced by the loose abrasive slurries. Those lower quality scratch edges may degrade the quality of the disks manufactured using lapping film for the texturing process.
Lapping films with polymeric film backings and porous nonwoven materials have both been used to polish magnetic media after the magnetic coatings have been applied. In contrast, the texturing process described above is performed before the magnetic coatings are applied to prepare the substrates to receive the magnetic coatings. The polishing minimizes the surface roughness of the magnetic coatings on the disks to allow for closer spacing of the computer head to the magnetic media. U.S. Pat. No. 4,762,534 discloses a method of polishing magnetic media using abrasive particles dispersed on a polymeric film, with voids between the abrasive particles to allow for removal of the magnetic oxides loosened during polishing. U.S. Pat. No. 4,983,421 discloses the use of a nonwoven material to polish the surface of metal thin-film type magnetic media. The nonwoven is used to buff the thin-film magnetic coating to reduce drop-outs and other errors in the magnetic coating.
Porous abrasive articles have also been used to polish magnetic oxide coated rigid memory disks. In that process, an abrasive article with a nonwoven backing and an abrasive composite is used to polish the surface of a rigid disk that has been coated with a magnetic oxide/resin composite. This polishing has, however, been used only to remove high spots in the magnetic oxide/resin composite to prevent the computer head from striking such high points.
To date, there has not been a method to uniformly texture thin film metal or metal alloy coated rigid disks before the application of the magnetic coatings in a clean process that generates high quality scratches and avoids the problem of reweld.